This invention relates to the technical domain of production of materials or composite parts that may or may not be conformed and that can be used directly or after transformation or association, particularly to form shaped structures or articles required in very many applications. More precisely, the purpose of the invention is a fibrous stiffener for making composite parts, that acts as a barrier for injected resins, and composite parts comprising such a stiffener.
Composite parts according to prior art usually combine at least one additional reinforcement, usually made of a textile or similar material, with a resin matrix usually of the thermosetting type, in which the said reinforcement is embedded so that it is present either within the thickness of the formed part or at the surface, in order to combine light weight with an acceptable mechanical strength.
It can be considered that these techniques are well controlled and are satisfactory in most applications. In other cases, it is desirable to have thick stiffeners required in some applications, for example plane or formed parts such as bodywork elements, pleasure boats, tanks or even aircraft. It has also been proposed that textile reinforcements like that described in patent FR 2 646 442 or in patent FR 2 734 847 could be used.
It is increasingly important to have simple and low cost techniques for making preforms for thick and lightweight walls or for large and lightweight bodies. When this type of preform is being designed, a thermosetting resin is injected in the liquid state adjacent to the stiffener arranged with the required form. Therefore it is essential to have a stiffener which, due to its nature, prevents the migration of resin through the stiffener before the resin polymerizes.
Furthermore, it is frequently desirable to inject different natures of resin on each side of the stiffener. For example, it is necessary to inject a resin such as a foaming resin in the central position of the composite part, to give the composite part the required volume while remaining light weight, and another resin performing a mechanizing function around the periphery in order to consolidate its external walls.
In general, it is necessary to make a first core in a first mould, for example by injecting polyurethane resin. This polyurethane core must then be sanded to make it adhesive, knowing that after the polyurethane surface has been molded its surface condition is smooth, after wax has been deposited. Finally, this polyurethane core is placed in a second mould with the textile stiffener to inject the second resin.
Therefore, it is usually necessary to make a preform composed of the polyurethane core associated with the fibrous stiffener used for the second injection. Therefore, composite parts are made in two molding steps with two slightly modified moulds, one for the first injection and the other for the second injection.